Are you participating in Manufacturing Day this year? It’s a day to open your doors and show what manufacturing is and isn’t. The event is a coordinated effort to address the skilled labor shortage and improve the public image of manufacturing. But before you register as a participant, you still have time to ensure your plant is running at optimal capacity.
Nothing would be more embarrassing than an unexpected breakdown while hosting a Manufacturing Day tour, which brings up Murphy's Law — any failure that can happen will, and at the worst possible time. One way to help reduce opportunities for failure is with precision alignment. Half of all breakdowns on rotating equipment stem from machinery misalignment. Soft foot can be a relatively common problem when you’re aligning machinery.
“Soft foot” is machine frame distortion, explains Alan Luedeking, vice president at Ludeca (www.ludeca.com). “The easiest way to ascertain if you have such a problem — with the machine stopped, locked, and tagged — is to loosen each anchor bolt individually, always with the others tight, and observe if any shaft movement takes place,” he says.
Using a dial indicator is another option. “Place a dial indicator of top of the machine foot being checked and zero it out,” offers Robert X. Perez, author of “Is My Machine OK?” If the dial indicator moves more than 0.001 in. when you loosen the foot’s hold-down bolt, you have a soft foot issue. “Retighten the bolt to see if the reading returns to zero,” he suggests. “If it does return to zero, you have proven the reading is repeatable and valid.”
On operating machines, try and pull on the shim packs under the feet with pliers, says Stan Riddle, trainer/technical support team at VibrAlign (www.vibralign.com). “If the shims move, there is probably a soft foot,” he explains. “A set of feeler gauges works equally well. I usually try to check two to three places on each foot with a 0.005-in. feeler gauge or shim. If it will fit under the foot, there is a soft foot present. I have seen shims that work their way out from under machine feet. Occasionally, it’s due to loose bolts, but more often than not, it is due to a soft foot.”
Prevention is always better than repairing, says Heinz Bloch, P.E., owner, Process Machinery Consulting in Westminster, Colorado. “I would use epoxy-filled base plates which, upon curing, are totally stiff and monolithic,” he suggests. “After curing, I would take a skim cut over the mounting pads. Upon installation, I would place magnet-base dial indicators and let the indicators look at the top of the machine's feet. Then I would tighten the hold-down bolts, and not with vise grips. Any indicator movement in excess of 0.002 in. is not acceptable. It would tell me that the machine manufacturer had perhaps not machined the bottom of the feet with sufficient accuracy or has given me a ‘green casting’ that has stress-relieved itself by warping.”
So, open your doors, but be prepared. Every day is a good day for proper alignment of rotating machinery.